1. Field of the Invention
The present invention relates to a microphone apparatus to be built into an appliance possessing an acoustic noise source or a vibration source therein.
2. Description of the Prior Art
In the collection of sound using a microphone, the quality of the sound signal deteriorates due to acoustic noise other than the desired sound, vibration noise caused by mechanical vibration and wind noise caused by wind. In particular, in an appliance such as a as video camera, not only does the mechanical system contained therein generate acoustic noise and vibration, but also the appliance itself is often used outdoors. When incorporating a directional microphone or a non-directional microphone in such an appliance, the S/N ratio of the sound collection drops owing to the following factors.
Since the microphone is close to the vibration source or acoustic noise source, the absolute level of the acoustic noise or vibration applied to the microphone increases.
Since the microphone is close to the acoustic noise source, a proximity effect occurs in a directional microphone, and the pressure sensitivity is raised in the front and rear directions thereof in the low frequency region so as to make it susceptible to the acoustic noise generated by the mechanical system.
The directional microphone is more liable to be influenced by vibrations than the non-directional microphone.
The directional microphone is more liable to be influenced by the wind than the non-directional microphone.
The non-directional microphone cannot eliminate acoustic noise by directivity.
A microphone apparatus having a function for reducing the wind noise has already been proposed (for example, see Japanese patent publication Nos. H01-39194 and H01-39195). The microphone apparatus comprises a non-directional microphone, a uni-directional microphone, a low pass filter for removing the high frequency components of the output signal of the non-directional microphone, a high pass filter for removing the low frequency components of the output signal of the uni-directional microphone, an adder for adding the outputs of the two filters, and a means for detecting the intensity of the wind noise.
In the thus composed microphone apparatus, by detecting the intensity of the wind noise, the wind noise is reduced by deriving the output signal of the uni-directional microphone when the wind is weak, and the combined signal of the high frequency components of the output signal of the uni-directional microphone and the low frequency components of the output signal of the non-directional microphone when the wind is strong.
In such a conventional microphone apparatus, however, although the wind noise can be reduced, if the apparatus is built into an appliance having a noise or vibration source, it is impossible to reduce the acoustic noise from increasing due to the proximity effect and mechanical vibration when the wind is weak.